But the Yellow River had flooded plenty of times before; the big difference now was that Mongol destruction magnified nature’s cruelties. In the 1230s famine and epidemic followed the Mongol armies, carrying off a million people around Kaifeng and perhaps even more in Sichuan, and in the 1270s the death toll was even worse. Overall, the four horsemen of the apocalypse that stalked China in the thirteenth
